1. Field of the Invention
The present invention relates to the power supply network of a printed circuit board for supplying power to logic cards or the like attached to a large scale computer or the like.
2. Description of the Prior Art
The network technique for supplying power to logic cards or the like constituting logic parts of a large scale computer is, for example, described in Japanese Publication of Unexamined Patent Application No. 61-139,099.
This document shows a structural example in which a plurality of logic cards (to be designated the loads, hereinafter) are connected on a back board (to be designated the printed circuit board, hereinafter), and describes the network technique of the power supply in which horizontal buses are attached on one plane of the printed circuit board in order to minimize the voltage drop occuring in the inside of the board when the plurality of the loads are supplied with current.
Referring to FIG. 2, the conventional technique will be described.
In FIG. 2, the printed circuit board 5 has loads l composed of a plurality of logic cards carrying logic elements, the loads l being attached to sockets 3 by means of lead pins 2 mounted on the loads l. Within the sockets 3, said lead pins 2 are electrically connected to contact points 4, and further the contact points 4 are connected to through hole network 6 formed in the inside of the board 5.
Said through hole network 6 is formed through the board 5, from a first principle plane of the board 5 where the loads l are attached to the other plane across the whole thickness, and is electrically connected to power supply pads 17 formed on the other plane respectively.
On the first principle plane of said board 5, main power supply pads 7 are formed in the vicinities of its peripheral edge, and secured by fixtures or bolts 10 to one end of a power cable 9 through which external power is supplied to the loads l.
In the inside of said board 5, power supply layer 8 is formed in parallel with the first principle plane substantially throughout the entire periphery. This power supply layer 8 is connected directly with each through hole network 6 at each of the stations, thereby an internal network being formed.
Said power supply layer 8 is, in the vicinity of its peripheral edge, connected directly with the through hole network 6 electrically connected to said main power supply pad 7. In this structure, the source voltage supplied through the cables for power supply 9 and the main power supply pads 7 is applied to each of the loads l through the power supply layer 8 and the through hole network 6.
Now, in the prior art shown in FIG. 2, horizontal buses 11, formed by working conductive metal such as aluminum (Al) into a frame-like shape, are secured to each of the power supply pads 17 by means of bolts 10, on the other plane of the board 5, to minimize the voltage drop across the main power supply pads 7 or the like and each of the loads l.
However, though said prior art is available as the means for decreasing the whole voltage drop in the inside of the board 5, there is no consideration for the dispersion in the voltage occurring among a plurality of the loads l.
Thus, the drop of voltage is extremely higher in the load l attached near the center of the first principle plane of the board l than in the load l attached near the peripheral edge because of the difference in the power supply path from said main power supply pad 7. Consequently, it is difficult to maintain the stability of the device operation, therefore, it must be necessary to take measures in which the allowable margin of the source voltage is broadened.